Minimally invasive bone anchor extensions

ABSTRACT

Methods and devices are provided for facilitating delivery and implanting of a bone anchor into bone. In one exemplary embodiment, a bone anchor extension is provided for coupling to a bone anchor to facilitate delivery and implanting of the bone anchor in bone. The bone anchor extension can have a generally elongate configuration that allows it to extend from a skin incision in a patient to a site proximate a patient&#39;s spine, and it can include a lumen extending therethrough between proximal and distal ends thereof. A distal end of the bone anchor extension can be adapted to engage a bone anchor, such as a bone screw. Various techniques are provided for locking the distal end of the bone anchor extension into engagement with a bone anchor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/539,504 filed on Oct. 6, 2006 and entitled “Minimally Invasive BoneAnchor Extensions,” which claims priority to U.S. ProvisionalApplication No. 60/827,000 filed on Sep. 26, 2006 and entitled“Minimally Invasive Bone Anchors Extensions,” which are herebyincorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to methods and devices for implanting boneanchors.

BACKGROUND OF THE INVENTION

For a number of known reasons, spinal fixation devices are used inorthopedic surgery to align and/or fix a desired relationship betweenadjacent vertebral bodies. Such devices typically include a spinalfixation element, such as a relatively rigid fixation rod or plate, thatis coupled to adjacent vertebrae by attaching the element to variousanchoring devices, such as hooks, bolts, wires, or screws. The fixationelements can have a predetermined contour that has been designedaccording to the properties of the target implantation site, and onceinstalled, the fixation element holds the vertebrae in a desired spatialrelationship, either until desired healing or spinal fusion has takenplace, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of thevertebrae. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a rod-receiving element,usually in the form of a U-shaped recess formed in the head. Aset-screw, plug, or similar type of closure mechanism is used to lockthe fixation element, e.g., a spinal rod, into the rod-receiving head ofthe pedicle screw. In use, the shank portion of each screw is threadedinto a vertebra, and once properly positioned, a rod is seated throughthe rod-receiving member of each screw and the rod is locked in place bytightening a cap or other closure mechanism to securely interconnecteach screw and the fixation rod.

Recently, the trend in spinal surgery has been moving toward providingminimally invasive devices and methods for implanting bone anchors andspinal fixation devices.

SUMMARY OF THE INVENTION

The present invention generally provides methods and devices forimplanting bone anchors and spinal fixation devices. In one embodiment,a percutaneous access device is provided having a hollow elongate memberwith an inner lumen extending therethrough and adapted to span from atleast a skin incision in a patient to a predetermined site proximate aspine of the patient. The hollow elongate member can include opposedarms coupled by at least one fulcrum such that the opposed arms areadapted to pivot relative to one another to releasably engage a boneanchor between a distal end of the opposed arms. The device can alsoinclude a locking mechanism disposed between the opposed arms andmovable between an unlocked position in which the opposed arms are freeto pivot relative to one another, and a locked position in which thelocking mechanism prevents the opposed arms from moving toward and awayfrom one another to lock a bone anchor into engagement with the opposedarms.

In one embodiment, the locking mechanism can be slidably coupled to thehollow elongate member such that the locking mechanism slides proximallyand distally between the unlocked and locked positions. The lockingmechanism can include, for example, at least one block extending betweenthe opposed arms and positioned proximal of the fulcrum. The block canbe formed on a band at least partially disposed around the hollowelongate member. The band can have various features. For example, theband can include a retaining element formed thereon and adapted toselectively retain the band in the locked and unlocked positions. In oneembodiment, the retaining element can be at least one deflectable tangformed on the band, and the hollow elongate member can include at leastone opening formed therein for receiving the deflectable tang. Inanother embodiment, the band can include an elongate arm extendingproximally therefrom and adapted to slidably move the band proximallyand distally along the hollow elongate member, and/or opposed extensionarms extending distally from the band and adapted to be positionedadjacent to a distal portion of the opposed arms when the block is inthe locked position to prevent outward deflection of the opposed arms.

In another embodiment, the locking mechanism can be rotatably coupled tothe hollow elongate member such that the locking mechanism rotatesbetween the locked and unlocked position. For example, the lockingmechanism can be a plug rotatably disposed within the hollow elongatemember. The plug can have an oblong shape that includes a maximumdiameter adapted to extend between the opposed arms when the plug is inthe locked position to prevent pivotal movement of the opposed arms, anda minimum diameter adapted to extend between the opposed arms when theplug is in the unlocked position to allow pivotal movement of theopposed arms.

The hollow elongate member can also have a variety of configurations. Inone embodiment, the hollow elongate member can include opposed first andsecond slots formed therein and extending proximally from a distal endof the hollow elongate member to define the opposed arms of the hollowelongate member. A first fulcrum can be disposed within the first slotand a second fulcrum can be disposed within the second slot. The opposedarms of the hollow elongate member can also include an engagementmechanism formed on a distal end thereof for engaging a bone anchor. Theengagement mechanism can be, for example, a lip formed on an innersurface of each of the opposed arms and adapted to engage acorresponding groove formed in a bone screw. The distal end of theopposed arms can also include an anti-rotation mechanism formed thereonfor preventing rotation of a bone anchor engaged between the opposedarms. The anti-rotation mechanism can be, for example, first and secondpins extending inward from opposed outer regions of the first arm, andfirst and second pins extending inward from opposed outer regions of thesecond arm.

A spinal anchoring system is also provided and can include a bone anchorhaving a head with a bone-engaging shank extending therefrom, and a boneanchor extension. The bone anchor extension can include a tubular memberadapted to span from at least a skin incision in a patient to apredetermined site proximate a spine of the patient. The tubular membercan have first and second opposed arms and an inner lumen extendingtherethrough between proximal and distal ends thereof. The first andsecond opposed arms can include a distal end adapted to pivot relativeto one another to releasably engage the head of the bone anchor. Thebone anchor extension can also include a locking mechanism coupled tothe tubular member and movable between an unlocked position in which theopposed arms are free to pivot relative to one another, and a lockedposition in which the locking mechanism is positioned between theopposed arms and prevents the opposed arms from moving toward and awayfrom one another thereby locking the opposed arms into engagement withthe head of the bone anchor. In an exemplary embodiment, the opposedarms can be pivotally coupled to one another by at least one fulcrum.The locking mechanism can be positioned proximal of the at least onefulcrum. The locking mechanism can be, for example, at least one blockadapted to extend into at least one slot formed between the opposed armswhen the locking mechanism is in the locked position. In anotherembodiment, the head of the bone anchor can include a groove formedtherein, and a distal end of the opposed arms can include a lip formedon an inner surface thereof and adapted to engage the groove formed inthe head to mate the bone anchor to the opposed arms.

Exemplary surgical methods are also provided, and in one embodiment themethod can include positioning a head of a bone anchor between a distalend of opposed arms of an extension device. The opposed arms can pivotrelative to one another to engage the head of the bone anchor. Themethod can also include moving a locking mechanism coupled to theextension device from an unlocked position in which the opposed arms arefree to pivot relative to one another, to a locked position in which thelocking mechanism extends between the opposed arms and prevents theopposed arms from pivoting relative to one another to lock the head ofthe bone anchor into engagement with the opposed arms. The method canalso include implanting the bone anchor in bone, preferably after thebone anchor is mated to the extension device. A spinal fixation elementcan also be positioned within the head of the bone anchor, and afastening element can be inserted through the extension device and matedto the head of the bone anchor to lock the spinal fixation elementwithin the head of the bone anchor. The locking mechanism can be movedfrom the locked position to the unlocked position to release the head ofthe bone anchor from the opposed arms of the extension device. In anexemplary embodiment, the locking mechanism is positioned between atissue surface and the bone anchor, and an actuator located above thetissue surface is actuated to move the locking mechanism. In anotherembodiment, moving the locking mechanism from the unlocked position tothe locked position can include sliding the locking mechanism along alongitudinal axis of the extension device. For example, the lockingmechanism can be slid from a proximal position to a distal position. Inyet another embodiment, moving the locking mechanism from the unlockedposition to the locked position can include rotating the lockingmechanism relative to the extension device.

In another embodiment, a bone anchor extension is provided and includesan inner tube having proximal and distal ends with a lumen extendingtherebetween, and an outer tube disposed about at least a portion of theinner tube and having proximal and distal ends with a lumen extendingtherebetween. The outer tube is sized to span from at least a skinincision in a patient to a predetermined site proximate a spine of thepatient. The bone anchor extension also includes a locking mechanismpivotally coupled to the inner and outer tubes such that pivotalmovement of the locking mechanism is effective to move the inner tuberelative to the outer tube to engage a bone anchor between the distalend of the inner tube and the distal end of the outer tube. In anexemplary embodiment, the locking mechanism is movable between a firstposition in which the locking mechanism extends longitudinally relativeto a longitudinal axis of the outer tube, and a second position in whichthe locking mechanism extends transversely outward relative to alongitudinal axis of the outer tube. For example, the inner and outertubes can be effective to engage and lock a bone anchor between thedistal ends thereof when the locking mechanism is in the first position,and a bone anchor can be released from the distal ends of the inner andouter tubes when the locking mechanism is in the second position.

In one exemplary embodiment, the locking mechanism can include an armpivotally coupled to the outer tube, and a linkage pivotally coupledbetween the arm and the inner tube such that pivotal movement of the armrelative to the outer tube is effective to pull the linkage to move theinner tube relative to the outer tube. The linkage can extend at anangle relative to a longitudinal axis of the outer tube to releasablylock the locking mechanism in the first position, and the arm can beeffective to pull the linkage and inner tube in a proximal directionrelative to the outer tube when the arm is moved from the first positionto the second position.

In another exemplary embodiment, the locking mechanism can include anarm having at least one cam formed thereon and disposed between theinner and outer tubes. The cam can be pivotally coupled to the outertube and disposed within at least one cut-out formed in the inner tubesuch that pivotal movement of the arm is effective to move the innertube relative to the outer tube. The inner tube can include opposedcut-outs formed in the proximal end thereof, and pivotal movement of thearm between the first and second positions can be effective to alter asize of the opposed cut-outs to thereby move the inner tube relative tothe outer tube. The device can also include a locking mechanism formedon at least one of the arm and the outer tube and effective toreleasably lock the arm in the first position. The locking mechanism canbe, for example, a plurality of teeth formed on the outer tube andadapted to engage the arm.

In other aspects, a spinal anchoring system is provided and includes abone anchor having a head with a bone-engaging shank extendingtherefrom, and a bone anchor extension having an inner tube havingproximal and distal ends with a lumen extending therebetween, and anouter tube disposed about at least a portion of the inner tube andhaving proximal and distal ends with a lumen extending therebetween. Theouter tube can be sized to span from at least a skin incision in apatient to a predetermined site proximate a spine of the patient. Thebone anchor extension can also include a locking mechanism pivotallycoupled to at least one of the inner and outer tubes and adapted topivot to move the inner tube relative to the outer tube to engage thehead of bone anchor between the distal end of the inner tube and thedistal end of the outer tube. In one embodiment, the locking mechanismcan include a cam disposed between the inner and outer tubes. The camcan be disposed within a cut-out formed in the inner tube, and it canhave a boss formed thereon and pivotally coupled to the outer tube. Inuse, the cam can be adapted to alter a size of the cut-out formed in theinner tube to thereby move the inner tube relative to the outer tube. Inanother embodiment, the locking mechanism can be movable between a firstposition, in which the locking mechanism extends longitudinally relativeto a longitudinal axis of the outer tube, and a second position in whichthe locking mechanism extends transversely outward relative to alongitudinal axis of the outer tube. The locking mechanism can be, forexample, an arm pivotally coupled to the outer tube and a linkagepivotally coupled between the arm and the inner tube. In use, pivotalmovement of the locking mechanism can be adapted to pull the linkageproximally to move the inner tube proximally relative to the outer tube.In an exemplary embodiment, the locking mechanism is coupled to aproximal end of the outer tube.

In yet another embodiment, a surgical method is provided and includespositioning a head of a bone anchor between a distal end of an outertube and a distal end of an inner tube disposed within the outer tube,and pivoting a locking mechanism pivotally coupled to a proximal portionof the outer tube to move the locking mechanism from an unlockedposition to a locked position and thereby slide the inner tube relativeto the outer tube to engage the head of the bone anchor between thedistal ends of the inner and outer tubes. The method can also includeimplanting the bone anchor in bone, positioning a spinal fixationelement within the head of the bone anchor, inserting a fasteningelement through the extension device, and mating the fastening elementto the head of the bone anchor to lock the spinal fixation elementwithin the head of the bone anchor. The method can further includemoving the locking mechanism from the locked position to the unlockedposition to release the head of the bone anchor from the distal ends ofthe inner and outer tubes. The locking mechanism can include, forexample, a cam that moves the inner tube relative to the outer tube, ora hinge that moves the inner tube relative to the outer tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a perspective view of one embodiment of a bone anchorextension having opposed pivoting arms for engaging a bore anchor, and asliding locking mechanism shown in the locked position for preventingpivotal movement of the opposed arms;

FIG. 1B is an exploded view of the bone anchor extension of FIG. 1A;

FIG. 1C is a cross-sectional view of the bone anchor extension of FIG.1A, showing the locking mechanism in an unlocked position;

FIG. 1D is a cross-sectional view of the bone anchor extension of FIG.1A, showing the locking mechanism in a locked position;

FIG. 1E is a side view of the bone anchor extension of FIG. 1A, showingtangs for maintaining the locking mechanism in a fixed position;

FIG. 1F is a cross-sectional view of the bone anchor extension of FIG.1E;

FIG. 2A is a perspective view of another embodiment of a bone anchorextension having opposed pivoting arms for engaging a bone anchor, and asliding locking mechanism shown in the locked position for preventingpivotal movement of the opposed arms;

FIG. 2B is a cross-sectional view of the bone anchor extension of FIG.2A, with the locking mechanism in the unlocked position;

FIG. 2C is a cross-sectional view of the bone anchor extension of FIG.2A, with the locking mechanism in the locked position;

FIG. 3A is a perspective view of yet another embodiment of a bone anchorextension having opposed pivoting arms for engaging a bone anchor, and asliding locking mechanism shown in the locked position for preventingpivotal movement of the opposed arms;

FIG. 3B is a side view of a distal portion of the device of FIG. 3A,showing a bone anchor coupled to a distal end of the device in theunlocked position;

FIG. 4A is a perspective view of another embodiment of a bone anchorextension having opposed pivoting arms for engaging a bone anchor;

FIG. 4B is a cross-sectional view of the bone anchor extension of FIG.4A, showing a rotating locking mechanism shown in the locked positionfor preventing pivotal movement of the opposed arms;

FIG. 5A is an exploded view of another embodiment of a bone anchorextension having opposed arms for engaging a bone anchor, and a hingedlocking mechanism shown in a locked position for locking a bone anchorbetween the opposed arms;

FIG. 5B is a side view of the bone anchor extension of FIG. 5A in theassembled configuration, showing the hinged locking mechanism in anunlocked position;

FIG. 5C is a side view of the bone anchor extension of FIG. 5A in theassembled configuration, showing the hinged locking mechanism in alocked position;

FIG. 5D is a cross-sectional view of the bone anchor extension of FIG.5B, taken along a longitudinal axis of the device;

FIG. 5E is a cross-sectional view of the bone anchor extension of FIG.5C, taken along a longitudinal axis of the device;

FIG. 6A is an exploded view of another embodiment of a bone anchorextension having opposed arms for engaging a bone anchor, and a camlocking mechanism for locking a bone anchor between the opposed arms;

FIG. 6B is a perspective view of the bone anchor extension of FIG. 6A inthe assembled configuration, showing the locking mechanism in anunlocked position;

FIG. 6C is a perspective view of the bone anchor extension of FIG. 6A inthe assembled configuration, showing the locking mechanism in a lockedposition;

FIG. 6D is a cross-sectional view of the bone anchor extension of FIG.6B, taken along a longitudinal axis of the device;

FIG. 6E is a cross-sectional view of the bone anchor extension of FIG.6C, taken along a longitudinal axis of the device;

FIG. 7A is a perspective view of a distal portion of a bone anchorextension positioned in relation to a bone anchor, showing the boneanchor extension in the unlocked position; and

FIG. 7B is a perspective view of the bone anchor extension and boneanchor of FIG. 7A, showing the bone anchor extension in the lockedposition.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those of ordinary skill in the art will understand that thedevices and methods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

The present invention generally provides methods and devices forfacilitating delivery and implanting of a bone anchor, such as a bonescrew, into bone, such as one or more vertebral bodies of the spine. Inone exemplary embodiment, a bone anchor extension is provided forcoupling to a bone anchor to facilitate delivery and implanting of thebone anchor in bone. The bone anchor extension can have a generallyelongate configuration that allows it to extend from a skin incision ina patient to a site proximate a patient's spine, and it can include alumen extending therethrough between proximal and distal ends thereof. Adistal end of the bone anchor extension can be adapted to engage a boneanchor, such as a bone screw. Various techniques are provided forlocking the distal end of the bone anchor extension into engagement witha bone anchor. In use, the bone anchor extension provides a percutaneouspathway between a skin incision and a bone anchor mated to the distalend of the bone anchor extension, thereby allowing components of thebone anchor, such as a fastening mechanism, a spinal fixation element,and/or other instruments to be delivered in a minimally invasive mannerto the bone anchor and surrounding surgical site. Although the methodsand devices disclosed herein are designed primarily for use in spinalapplications, one skilled in the art will appreciate that the methodsand devices can be used to facilitate the implantation of any type ofbone anchor to any type of bone.

FIGS. 1A-1F illustrate one exemplary embodiment of a bone anchorextension for use in delivering and implanting bone anchors in bone,such as one or more vertebral bodies of the spine. The bone anchorextension generally includes a hollow elongate member 12 having an innerlumen 120 extending therethrough and adapted to span from at least askin incision in a patient to a predetermined site proximate a spine ofthe patient. The hollow elongate member 12 has opposed arms 12 a, 12 bthat are coupled by at least one fulcrum such that the opposed arms 12a, 12 b are adapted to pivot relative to one another, i.e., to movetoward and away from one another, to releasably engage a bone anchorbetween a distal end 12 d of the opposed arms 12 a, 12 b. The boneanchor extension 10 also includes a locking mechanism 14 disposedbetween the opposed arms 12 a, 12 b and movable between an unlockedposition in which the opposed arms 12 a, 12 b are free to pivot relativeto one another, and a locked position in which the locking mechanism 14prevents pivotal movement of the opposed arms 12 a, 12 b to lock a boneanchor into engagement with the opposed arms 12 a, 12 b.

The elongate member 12 can have a variety of configurations. In theillustrated embodiment, the elongate member 12 has a generallycylindrical shape with an inner lumen 12 o extending therethroughbetween proximal and distal ends 12 a, 12 b thereof. Opposed slots 16 a,16 b are formed in the hollow elongate member 12 and they extend alongvarious portions of the length of the elongate member 12 to separate theelongate member 12 into two halves, each of which forms an arm 12 a, 12b. The opposed arms 12 a, 12 b are configured to engage a bone anchor,such as a bone screw, between the distal ends 12 d thereof. Whilevarious techniques can be used to allow the arms 12 a, 12 b to engage abone anchor, in an exemplary embodiment the arms 12 a, 12 b arepivotally coupled to one another such that the distal ends 12 d of thearms 12 a, 12 b can pivot between open and closed positions. As shown inFIGS. 1A-1F, the opposed arms 12 a, 12 b are connected to one another ata pivot point P₁ that is located adjacent to, but proximal of the distalend 12 d of the elongate member 12. The pivot point P₁ includes a hingeextending across the opposed slots 16 a, 16 b and between the opposedarms 12 a, 12 b, and a fulcrum positioned between each arm 12 a, 12 b.The hinge can be defined by the shape of the slots 16 a, 16 b formed inthe elongate member 12. In the illustrated embodiment slots 16 a, 16 bdo not extend through the pivot point P₁, leaving a portion thatconnects the arms 12 a, 12 b. In particular, as best shown in FIGS.1E-1F, the distal portion of the slots 16 a, 16 b each include anenlarged, curved terminal end 17 a, 17 b located adjacent to the pivotpoint P₁. A second curved slot 20 a, 20 b can also be formed adjacent tothe curved terminal end 17 a, 17 b of the distal portion of each slot 16a, 16 b to define a curved spring 21 a, 21 b that extends between thearms 12 a, 12 b. The curved spring 21 a, 21 b will allow the arms 12 a,12 b to extend away from and toward one another, thereby allowingpivotal movement of the arms 12 a, 12 b. As indicated above, the pivotpoint P₁ can also include a fulcrum disposed between the arms 12 a, 12 bsuch that the arms 12 a, 12 b will pivot about the fulcrum. In theillustrated embodiment, the fulcrum is in the form of first and secondblocks 22 a, 22 b (FIG. 1B) that are positioned between the arms 12 a,12 b just proximal to the springs 21 a, 21 b. In use, movement of theproximal portion of each arm 12 a, 12 b toward one another will causethe distal portion of each arm 12 a, 12 b to move away from one another,and vice versa, thereby allowing a bone anchor to be engaged between thedistal ends 12 d of the arms 12 a, 12 b.

In order to facilitate engagement of a bone anchor between the distalends 12 d of the arms 12 a, 12 b, the arms 12 a, 12 b can include anengagement mechanism formed thereon. While various engagement mechanismscan be used, in one exemplary embodiment each arm 12 a, 12 b can includea lip 18 a, 18 b formed on an inner surface thereof and adapted to bereceived within and to engage a corresponding groove formed in a boneanchor, such as a bone screw. In use, the distal portion of the arms 12a, 12 b can pivot away from one another to allow the arms 12 a, 12 b tobe positioned around the bone anchor, and they can pivot toward oneanother to allow the lips 18 a, 18 b to extend into and engage thecorresponding grooves in the bone anchor, thereby mating the bone anchorextension 10 to the bone anchor. The arms 12 a, 12 b can also includevarious other features, such as an anti-rotation mechanism formed on adistal end 12 d of the opposed arms 12 a, 12 b for preventing rotationof a bone anchor engaged between the opposed arms 12 a, 12 b. In oneembodiment as shown in FIGS. 1A and 1B, the anti-rotation mechanism canbe in the form of first and second pins 24 a, 24 b extending inward fromopposed outer regions of the first arm 12 a, and first and second pins26 a, 26 b extending inward from opposed outer regions of the second arm12 b. The pins can be positioned to extend into opposed slots fanned ina bone anchor, thus engaging the bone anchor therebetween to preventrotation of the bone anchor relative to the bone anchor extension 10. Aperson skilled in the art will appreciate that a variety of othertechniques can be used to mate the bone anchor extension 10 to a boneanchor, and that the particular configuration of the engagementmechanism can vary depending on the configuration of the bone anchor.

As previously indicated, the bone anchor extension 10 can also include alocking mechanism that is adapted to lock a bone anchor into engagementwith the bone anchor extension 10, thereby preventing inadvertentdisengagement of the bone anchor extension 10 from the bone anchorduring use of the device. In the embodiment shown in FIGS. 1A-1F, thelocking mechanism is in the form of a single or unitary locking band 14that is adapted to slidably move along the elongate member 12 between anunlocked position in which the locking band 14 allows free pivotalmovement of the opposed arms 12 a, 12 b relative to one another, and alocked position in which the locking band 14 prevents pivotal movementof the opposed arms 12 a, 12 b relative to one another to lock a boneanchor into engagement with the distal ends 12 d of the arms 12 a, 12 b.As best shown in FIG. 1B, the locking band 14 has a generally annularshape and includes opposed protrusions or blocks 27 a, 27 b formed on aninner surface thereof. Each block 27 a, 27 b is shaped to extend betweenthe opposed slots 16 a, 16 b formed in the elongate member 12. In orderfor the blocks 27 a, 27 b to allow free pivotal movement of the arms 12a, 12 b when the blocks 27 a, 27 b are located in an unlocked positionand to prevent pivotal movement of the arms 12 a, 12 b when the blocks27 a, 27 b are located in a locked position, a width between the opposedslots 16 a, 16 b formed in the elongate member 12 can vary. Inparticular, as shown in FIGS. 1C and 1D, the proximal portion of theslots 16 a, 16 b can decrease in width just proximal of and adjacent tothe pivot point P₁ to form a narrowed region 17. The blocks 27 a, 27 bcan have a width that is substantially the same as the width of thenarrowed region 17. As a result, when the blocks 27 a, 27 b on thelocking band 14 are located proximal of the narrowed region 17, i.e.,when the locking band 14 is in a proximal position, the anus 12 a, 12 bcan pivot freely to allow the distal ends 12 d of the arms 12 a, 12 b tobe positioned around a bone anchor. FIG. 1C illustrates the locking band14 in the proximal unlocked position with the block 27 b positionedproximal of the narrowed region 17. When the locking band 14 is sliddistally along the elongate member 12, the blocks 27 a, 27 b can extendinto the narrowed region 12 and between the opposed arms 12 a, 12 b. Theblocks 27 a, 27 b will thus prevent pivotal movement of the opposed arms12 a, 12 b about the blocks 22 a, 22 b that form the fulcrum, therebylocking the arms 12 a, 12 b in a fixed position. Since the distalportion of the arms 12 a, 12 b cannot move away from one another, a boneanchor engaged between the distal ends 12 d of the arms 12 a, 12 b willbe locked therebetween. The distal portion of the arms 12 a, 12 b arealso prevented from moving toward one another as well due to theconfiguration of the locking band 14. FIG. 1D illustrates the lockingband 14 in the distal locked position with the block 27 b is positionedwithin the narrowed region 17 to prevent pivotal movement of the arms 12a, 12 b.

In order to maintain the locking band 14 in the proximal unlockedposition and the distal locked position, the locking band 14 can alsoinclude an engagement mechanism formed thereon for releasably engagingthe elongate member 12. As shown in FIG. 1B, the locking band 14includes opposed deflectable tangs 28 a, 28 b formed thereon. The tangs28 a, 28 b, for example, can be formed by cut-outs in the locking band14. Each tang 28 a, 28 b can include a protrusion 29 a, 29 b formed on adistal end thereof and adapted to extend into a corresponding detent oropening formed in the elongate member 12. FIG. 1B illustrates proximaland distal openings 30 a, 30 b formed in arm 12 a. While not shown, theother arm 12 b can likewise include proximal and distal openings formedtherein. When the locking band 14 is in the proximal unlocked position,the protrusion 29 a, 29 b on each tang 28 a, 28 b can extend into theproximal opening in each arm 12 a, 12 b, thereby engaging the elongatemember 12 and thus maintaining the locking band 14 in the proximalunlocked position. When a force is applied to the locking band 14 toslide the locking band 14 distally, the arms 12 a, 12 b will deflectoutward to remove the protrusions 29 a, 29 b from the openings. When thelocking band 14 is in the distal position, i.e., when the blocks 27 a,27 b are located within the narrowed region 17 of the slots 16 a, 16 b,the protrusions 29 a, 29 b on the tangs 28 a, 28 b will extend into andengage the distal openings in the arms 12 a, 12 b to maintain thelocking band 14 in the distal locked position. FIGS. 1E and 1Fillustrate the locking band 14 in the distal locked position, showingprotrusion 29 a extending into the distal opening 30 b formed in arm 12a. Again, a force can be applied to the locking band 14 to cause thearms 12 a, 12 b to deflect outward and thereby allow the locking band 14to be slid proximally to return to the proximal unlocked position.

In use, since the bone anchor extension is preferably inserted through askin incision and extends to an anchor site, only a proximal portion ofthe bone anchor extension will extend outside of the patient's body.Thus, an actuator, such as a driver tool, grasper, or other device, canbe inserted through or along side the elongate member, and it can beused to engage the locking band to slide it between the proximal anddistal positions. Alternatively, the actuator can be formed on thelocking band. For example, the locking band can include an extension armor handle formed thereon and configured to be grasped by a user at theproximal end of the device. FIGS. 2A-2C illustrate one exemplaryembodiment of a bone anchor extension 100 having a locking band 114 thatis similar to the locking band 14 shown in FIGS. 1A-1F, but thatincludes an elongate extension arm 115 formed thereon. In particular,the arm 115 is mated to or integrally formed on a portion of the lockingband 114, and it extends in a proximal direction along an outer surfaceof one of the arms 112 a, 112 b of the elongate member 112. A proximalend 115 p of the extension arm 115 can extend proximally beyond aproximal end 112 p of the elongate member 112, thus allowing a user tograsp the proximal end 115 p of the extension arm 115. The user can thusmove the arm 115 proximally and distally, thereby sliding the lockingband 114 between the unlocked and locked positions.

FIGS. 2A-2C also illustrate an alternative embodiment of a locking band114. In this embodiment, the locking band 114 is not annular, but ratheris substantially C-shaped such that it extends around only a portion ofthe elongate member 112. The locking band 114 still functions similar tothe locking band 14 shown in FIGS. 1A-1F. In particular, locking band114 includes a block 126 formed on an inner surface thereof as shown inFIG. 2C. When the locking band 114 is in the proximal position, as shownin FIGS. 2A and 2B, the block will be positioned proximal of thenarrowed region 117 of the opposed slots 116 a, 116 b, thus allowingfree pivotal movement of the opposed arm 112 a, 112 b. When the lockingband 114 is moved distally into the distal locked position, as shown inFIG. 2C, the block 126 will be positioned within the narrowed region 117and just proximal of the block 122 that forms the fulcrum, thuspreventing pivotal movement of the opposed arms 112 a, 112 b and lockinga bone anchor between the distal ends of the arms 112 a, 112 b.

The locking band can also include features to further preventdisengagement between a bone anchor and the distal ends of the opposedarms of the elongate member. FIGS. 3A-3B illustrate another embodimentof a bone anchor extension 200 having a locking band 214 that is similarto the locking bands 14, 114 shown in the previous embodiments, but thatincludes opposed extension arms 215 a, 215 b extending distally from theband 214. When the locking band 214 is in the proximal unlockedposition, as shown in FIG. 3A, the extension arms 215 a, 215 b will bepositioned adjacent to or proximal of the pivot point P₂ so as to notinterfere with pivotal movement of the arms 212 a, 212 b of the elongatemember 212. When the locking band 214 is moved to the distal positionthe extension arms 215 a, 215 b will be positioned adjacent to a distalportion of the opposed arms 212 a, 212 b of the elongate member 212. Asa result, the extension aims 215 a, 215 b will help prevent outwarddeflection of the distal end 212 d of the opposed arms 212 a, 212 b ofthe elongate member 212, thereby further preventing disengagementbetween a bone anchor and the bone anchor extension 200.

FIG. 3B also illustrates an exemplary bone anchor 250 that is matable toa distal end of the bone anchor extensions of FIGS. 1A-4B. By way ofnon-limiting example, the bone anchor 250 is shown coupled to the boneanchor extension 200 of FIG. 3B. One skilled in the art will appreciate,however, that the bone anchor extensions disclosed herein are notlimited to use with the illustrated bone anchor 250 but instead may beconfigured for use with any type of bone anchor, e.g., bone screw orhook; mono-axial or polyaxial.

In general, the bone anchor 250 includes a receiving member or head 252that is configured to receive and couple a spinal fixation element, suchas a spinal rod or spinal plate, to bone, and a distal bone engagingportion 254, such as an externally threaded screw shank. The head 252 ofthe bone screw 250 has a generally U-shaped configuration with opposedarms 252 a, 252 b and opposed U-shaped slots formed between the arms 252a, 252 b. The slots are configured to receive a spinal fixation element,such as a spinal rod. In order to mate the bone screw 250 to the distalend 212 d of the bone anchor extension 200, the proximal end of the head252 can include at least one groove formed radially around at least aportion of an outer surface of each arm 252 a, 252 b of the head 252.Each groove is adapted to receive a corresponding lip formed on an innersurface of the distal end 212 d of each arm 212 a, 212 b of the boneanchor extension 200. The lips can be positioned within the grooves bysqueezing a proximal end of the arms 212 a, 212 b toward one another toopen or expand the distal portion of the arms 212 a, 212 b. The arms 212a, 212 b can then be released to allow the distal ends 212 d to cometogether and engage the head 252. Once mated, the locking band 214 canbe moved to the locked position to lock the bone anchor 250 intoengagement with the bone anchor extension 200, thereby preventingseparation of the bone anchor extension 200 and bone anchor 250 untildesired.

A person skilled in the art will appreciate that the locking mechanismcan have a variety of other configurations. FIGS. 4A-4B illustrateanother embodiment of a bone anchor extension 300 that is similar to thebone anchor extensions described above with respect to FIGS. 1A-3B. Inthis embodiment, however, the locking mechanism is in the form of a plug314, rather than a locking band. As shown in FIG. 4B, the plug 314 isrotatably disposed within a cavity 313 formed in the hollow elongatemember 312 and located just proximal to the pivot point P₃, i.e.,proximal to the blocks that formed the fulcrum. The cavity 313 canmerely be a cut-out or groove formed on an inner surface of each arm 312a, 312 b. The plug 314 can have an asymmetrical shape, such as an oblongor oval shape, such that the plug 314 includes a maximum diameter and aminimum diameter. When the minimum diameter of the plug 314 is alignedwith and extends between the opposed arms 312 a, 312 b, and the maximumdiameter of the plug 314 is aligned with and extends between the opposedslots 316 a, 316 b, the plug 314 will be in the unlocked position toallow pivotal movement of the opposed arms 312 a, 312 b. The differencebetween the minimum diameter of the plug 314 and the diameter or widthof the cavity 313 formed in the opposed arms 312 a, 312 b will providespace that allows the arms 312 a, 312 b to pivot. When the plug 314 isrotated to position the maximum diameter of the plug 314 to extendbetween the opposed arms 312 a, 312 b, and the minimum diameter of theplug 314 to extend between the opposed slots 316 a, 316 b, the plug 314will be in the locked position to prevent pivotal movement of theopposed arms 312 a, 312 b. In other words, the maximum diameter of theplug 314 will extend between and be in contact with the cavity 313formed in the opposed arms 312 a, 312 b such that the plug 314 does notprovide any space to allow the arms 312 a, 312 b to pivot.

Various techniques can be used to maintain the plug 314 between theopposed arms 312 a, 312 b. In one embodiment, the cavity 313 in theopposed arms 312 a, 312 b can have a depth that captures the plug 314therein, even when the plug 314 is in the unlocked position. In anotherembodiment, the cavity 313 can include a dovetail configuration thatmates with a corresponding dovetail formed on the plug 314, thusallowing the plug 314 to rotate while preventing proximal and distalmovement of the plug 314 relative to the elongate member 312. In yetanother embodiment, the plug 314 could include a groove formed around aperimeter thereof, and one or both aims 312 a, 312 b can include a pinextending therethrough and slidably disposed within the groove in theplug 314. The pin(s) will thus allow rotatable movement of the plug 314while preventing proximal and distal movement of the plug 314 relativeto the arms 312 a, 312 b of the elongate member 31.

Various techniques can also be used to rotate the plug 314 between thelocked and unlocked positions. For example, in one embodiment the plug314 can include an opening or bore extending therethrough. The openingor bore can have an asymmetrical shape, such as a hexagonal shape, thatallows a complementary driver mechanism to extend into the opening orbore and thereby engage and rotate the plug 314. In an exemplaryembodiment, the opening or bore can have a size that is sufficient toallow a locking mechanism, such as a set screw for locking a spinalfixation element within a bone anchor, to be passed therethrough anddelivered to the bone anchor engaged by the distal end of each arm 312a, 312 b of the elongate member 312. A person skilled in the art willappreciate that a variety of other techniques can be used to rotate theplug 314 during use of the bone anchor extension.

FIGS. 5A-5E illustrate another embodiment of a bone anchor extension 400for use in delivering and implanting bone anchors in bone, such as oneor more vertebral bodies of the spine. In this embodiment, the boneanchor extension 400 generally includes an inner tube 402 havingproximal and distal ends 402 p, 402 d with a lumen 402 c extendingtherebetween, and an outer tube 404 that is disposed about at least aportion of the inner tube 402. The outer tube 404 can have proximal anddistal ends 404 p, 404 d with a lumen 404 c extending therebetween, andit can be sized to span from at least a skin incision in a patient to apredetermined site proximate a spine of the patient. The bone anchorextension 400 can also include a locking mechanism 410 that is coupledto the inner and outer tubes 402, 404 such that movement of the lockingmechanism is effective to move the inner tube 402 relative to the outertube 404 to engage a bone anchor between the distal end 402 d of theinner tube 402 and the distal end 404 d of the outer tube 404.

The inner and outer tubes 402, 404 can each have a variety ofconfigurations. In the illustrated embodiment, the inner and outer tubes402, 404 are generally cylindrical and the outer tube 404 is slidablydisposed around the inner tube 402 such that the tubes 402, 404 arecoaxial. The axial length of the inner and outer tubes 402, 404 can alsovary depending on, for example, the patient anatomy, the proceduresemployed, and/or, the area of the spine in which the device is employed.The inner and outer tubes 402, 404 can also be linear, as in theillustrated embodiment, or they can be curved or angled along one ormore sections or the entire length thereof. The inner and outer tubes402, 404 can be constructed from any suitable biocompatible material,including, for example, a metal, such as stainless steel, or a polymer,from any conventional method of manufacturing medical devices. A personskilled in the art will appreciate that the inner and outer tubes 402,404 can have various other configurations, including variouscross-sectional geometries. Moreover, the tubes 402, 404 need not becoaxial, and the bone anchor extension 400 can include any number oftubes.

As best shown in FIG. 5A, each tube 402, 404 can also include opposedelongate slots (FIG. 5A illustrates slots 406, 408) formed therein andextending from a distal end 402 d, 404 d thereof and terminating distalof a proximal end 402 p, 404 p thereof. The slots 406, 408 defineopposed arms 402 a, 402 b, 404 a, 404 b of each tube 402, 404, and theycan function to allow various tools and devices, such as spinal fixationelements, to be passed therethrough. Prior to locking, the slots 406,408 can also allow the arms 402 a, 402 b, 404 a, 404 b to deflectrelative to one another to facilitate engagement of a bone anchorbetween the distal ends 402 d, 404 d of the tubes 402, 404. Tofacilitate positioning of a spinal fixation element, the slots 406, 408in each tube 402, 404 are preferably aligned with one another along atleast a portion of the longitudinal axis of the device 400. The widthand length of the slots 406, 408 can vary depending on the particularmethods, instruments, and fixation elements being employed. In oneexemplary embodiment, for example, the length of the slots 406, 408 isselected to span at least from the skin incision to the distal end 402e, 404 d of the inner and outer tubes 402, 404. In such embodiments, theslots 406, 408 can be accessible from outside of the patient. In anotherexemplary embodiment, the length of the slots 406, 408 is selected tospan from the distal end 402 a, 402 d of the inner and outer tubes 402,404 to a point distal to the skin incision. In such embodiments, theslots 406, 408 can be accessible only from the lumens of the inner andouter tubes 402, 404. A person skilled in the art will appreciate thatthe quantity and configuration of the slots can vary, and that the tubesneed not include slots.

As previously indicated, the distal end 402 d, 404 d of the inner andouter tubes 402, 404 can be configured to engage a bone anchortherebetween. While various engagement techniques can be used, in oneexemplary embodiment the inner and outer tubes 402, 404 can releasablyengage a bone anchor in a manner that allows the bone anchor extension400 to be connected to the bone anchor during use, e.g., duringimplantation and/or delivery and/or fastening of a spinal fixationelement to the bone anchor, and that allows the bone anchor extension400 to be disconnected from the bone anchor at the conclusion of theprocedure. Preferably, the bone anchor extension can be disconnectedremotely, e.g., by manipulation of the proximal end of the bone anchorextension 400, as will be discussed in more detail below.

As shown in FIGS. 5A, 5D, and 5E, in one exemplary embodiment the distalend 404 d of the outer tube 404 can include a projection or lip 418 a,418 b formed on an inner facing surface of each arm 404 a, 404 b forengaging corresponding grooves formed in a bone anchor. In use, the arms404 a, 404 b can be rotated relative to the bone anchor to slide thelips into the grooves in the bone anchor, as will be described in moredetail with respect to FIGS. 7A and 7B. In other embodiments, the armscan flex in the radial direction to facilitate connection to a boneanchor. For example, the arms 404 a, 404 b can be flexed apart in theradial direction from a first, relaxed position to facilitateadvancement of the arms 404 a, 404 b longitudinally over a portion ofthe bone anchor. Once positioned about a portion of the bone anchor, thearms 404 a, 404 b can provide a radially compressive force on the boneanchor as the arms 404 a, 404 b attempt to return to the first, relaxedposition. A person skilled in the art will appreciate that the size,shape, and number of projections formed on each arm 404 a, 404 b canvary depending on, for example, the opening(s) provided on the boneanchor and the type of connection desired.

As further shown in FIGS. 5A, 5D, and 5E, the distal end 402 d of theinner tube 402 can include a contact surface 410 a, 410 b formed on eacharm 402 a, 402 b that is configured to contact at least a portion of abone anchor when the inner tube 402 is in the second position, as willbe discussed in more detail below. In the illustrated embodiment, thedistal end 402 d of the inner tube 402 has two opposed generally arcuatecontact surfaces 410 a, 410 b. The contact surfaces 410 a, 410 b areoriented approximately perpendicular to the longitudinal axis of theinner tube 402 and they are configured to contact a generally arcuatecontact surface provided on the proximal end of the bone anchor. In anexemplary embodiment, each contact surface 410 a, 410 b is complementaryin size, shape, and orientation to the contact surface on the boneanchor. One skilled in the art will appreciate that the configuration ofeach contact surface, e.g., number, size, shape, and orientation of thecontact surface, may vary depending on the configuration of the boneanchor.

The distal end 402 d of the inner tube 402 and/or the distal end 404 dof the outer tube 404 can also optionally include an anti-rotationmechanism configured to inhibit rotation of the bone anchor relative tothe bone anchor extension 400. For example, the distal end 402 d of theinner tube 402 can include one or more finger-like extensions thatextend approximately axially from the distal end 402 d of the inner tube402 and that engage a bone anchor to inhibit rotation of the bone anchorrelative to the bone anchor extension. FIG. 5A illustrates opposedextensions 412 a, 412 b formed on the first arm 402 a, and opposedextensions 414 a, 414 b formed on the second arm 402 b. The extension(s)can sit within a groove, recess, slot, or similar structure provided inthe bone anchor. Alternatively, the extension(s) can include a contactsurface for contacting an axially extending surface of the bone anchor.

As indicated above, the bone anchor extension 400 can also include alocking mechanism for longitudinally adjusting the inner tube 402relative to the outer tube 404. In an exemplary embodiment, the innertube 402 is adjustable between a proximal unlocked position in which thedistal end 402 d of the inner tube 402 is positioned proximal to thedistal end 404 d of the outer tube 404 as illustrated in FIGS. 5B and5D, and a distal locked position in which the distal end 402 d of theinner tube 402 is positioned proximate to the distal end 404 d of theouter tube 404, as shown in FIGS. 5C and 5E. In an exemplary embodiment,the distal end 402 d of the inner tube 402 contacts at least a portionof a bone anchor captured by the outer tube 404 when the inner tube 402is in the distal locked position to engage the bone anchor therebetween.A person skilled in the art will appreciate, however, that various otherengagement mechanisms can be used.

While the locking mechanism can have a variety of configurations, in oneexemplary embodiment, as shown in FIGS. 5A-5E, the locking mechanism canbe in the form of a hinge that is pivotally coupled to the inner andouter tubes 402, 404 such that pivotal movement of the locking mechanismis effective to move the inner tube 402 relative to the outer tube 404to engage a bone anchor between the distal end 402 d of the inner tube402 and the distal end 404 d of the outer tube 404. As shown, the hingegenerally includes an arm 420 that is pivotally coupled to the outertube 404, and a linkage 422 that is pivotally coupled between the arm420 and the inner tube 402. The arm 420 can have various shapes andsizes. For example, in the illustrated embodiment the arm 420 has agenerally elongate configuration and includes a proximal portion 420 pthat is positioned on one side of the outer tube 404, and a distalportion 420 d that is positioned on an opposite side of the outer tube404. A first pivot point X₁ is located between the proximal and distalportions 420 p, 420 d, and the arm 420 is pivotally attached to theouter tube 404 at the first pivot point X₁. As indicated above, thehinge also includes a linkage 422 that is coupled between the arm 420and the inner tube 402. The linkage 422 can have a variety ofconfigurations, but in the illustrated embodiment the linkage 422 is inthe form of an elongate member having proximal and distal ends 422 p,422 d. The proximal end 422 p of the linkage 422 is pivotally coupled toa terminal end of the distal portion 420 d of the arm 420 to form asecond pivot point X₂ on the hinge, and the distal end 422 d of thelinkage 422 is pivotally coupled to the inner tube 402 to form a thirdpivot point X₃ on the hinge. In use, when the proximal and distalportions 420 p, 420 d of the arm 420 are positioned at an angle relativeto a longitudinal axis of the outer tube 404, the linkage 422 and theinner tube 402 coupled thereto will be in a proximal unlocked position.As explained above, in the proximal unlocked position the distal end 402d of the inner tube 402 is positioned proximal of the distal end 404 dof the outer tube 404, as shown in FIGS. 5B and 5D. When the proximalportion 420 p of the arm 420 is moved toward and into longitudinalalignment with the outer tube 404, the distal portion 420 d of the arm420 will likewise move toward and into longitudinal alignment with theouter tube 404. The distal portion 420 d of the arm 420 will thus pushthe linkage 422 into longitudinal alignment with the inner and outertubes 402, 404, thereby causing the linkage 422 and the inner tube 402coupled thereto to move distally. Once the arm 420 is in longitudinalalignment with the outer tube 404, the inner tube 402 will be in thedistal locked position, as shown in FIGS. 5C and 5E. In this position, abone anchor can be engaged between the distal ends 402 d, 404 d of theinner and outer tubes 402, 404. As further shown in FIGS. 5A-5E, thelinkage 422 can extend beyond a longitudinal axis of the inner and outertubes 402, 404 as it is moved from the unlocked position to lockedposition such that the linkage 422 extends at a slight angle when thearm 420 is in the distal locked position. Such a configuration will helpmaintain the hinge in the locked position. A person skilled in the artwill appreciate that the hinge can have a variety of otherconfigurations.

As further shown in FIG. 5A, the bone anchor extension 400 can alsoinclude features to relieve any stress applied to the hinge. Forexample, a proximal portion of the inner tube 402 can include a reliefslit formed thereon and configured to provide relief to the stressapplied to the hinge when the hinge is in the locked position. While therelief slit can have a variety of configurations, and it can be locatedon various portions of the device, in the illustrated embodiment therelief slit is in the faun of a spiral cut slit 430 extending radiallyaround a proximal end of the inner tube 402. In use, when the hinge isin the locked position, the inner tube 402 will extend between the hingeand a bone anchor engaged between the distal ends 402 d, 404 d of theinner and outer tubes 402, 404. The relief slit 430 will compress,decreasing a length of the inner tube 402, to relieve any stress appliedto the hinge due to the locking connection between the proximal end 402p of the inner tube 402 and the hinge and the distal end 402 d of theinner tube 402 and the bone anchor.

FIGS. 6A-6E illustrate another embodiment of a bone anchor extension 500having a locking mechanism for moving an inner tube 502 relative to theouter tube 504 to engage a bone anchor between the distal ends 502 d,504 d of the inner and outer tubes 502, 504. In this embodiment, ratherthan having a hinge that pivots to push and pull the inner tube 502relative to the outer tube 504, the device 500 includes a lockingmechanism 510 that pivots to cam the inner tube 502 proximally anddistally relative to the outer tube 504. In general, the lockingmechanism 510 includes first and second arms 512, 514 that extend alongopposed sides of the outer tube 504, and that each include a proximalend 512 p, 514 p and a distal end in the form of a cam 512 d, 514 d. Thecam 512 d, 514 d on each arm 512, 514 can have various shapes and sizes,but is preferably asymmetrical. As shown in FIG. 6A, each cam 512 d, 514d is in the form of an oblong or oval shaped member. Each cam 512 d, 514d also includes a boss 512 b, 514 b formed on an outer surface thereofthat sits within a cut-out formed in the outer tube 504, and aprotrusion (only one protrusion 512 c is shown in FIG. 6A) formedthereon that sits within a cut-out formed in the inner tube 502. Eachboss and protrusion is configured to pivot relative to the outer andinner tubes 504, 502, respectively, to allow the arms 512, 514 to movebetween an unlocked position in which the arms 512, 514 extendtransversely outward, i.e., at an angle, relative to a longitudinal axisof the outer tube 504, and a locked position in which the arms 512, 514are longitudinally aligned with a longitudinal axis of the outer tube504. As each boss and protrusion pivots, the cams 512 d, 514 d force theinner tube 502 to move relative to the outer tube 504. In particular,when the arms 512, 514 are positioned to extend transversely outwardfrom the outer tube 504, i.e., when the arms 512, 514 are positioned atan angle relative to a longitudinal axis of the outer tube 504 as shownin FIG. 6D, each cam 512 d, 514 d will be in the first unlockedposition. In this position, a minimum diameter of each cam 512 d, 514 dwill extend along the longitudinal axis of the device, and a maximumdiameter of each cam 512 d, 514 d will extend substantiallyperpendicular to the longitudinal axis of the device. When the arms 512,514 are pivoted toward the outer tube 504 to longitudinally align thearms 512, 514 with the outer tube 504, as shown in FIG. 6E, the cams 512d, 514 d will rotate relative to the inner and outer tubes 502, 504. Asthe maximum diameter of each cam 512 d, 514 d approaches alignment withthe longitudinal axis, the increasing diameter of each cam 512 d, 514 dwill cause the inner tube 502 to move distally relative to the outertube 504. In particular, the outer surface of the inner tube 502includes an abutment (only one abutment 503 a is shown in FIGS. 6A, 6D,and 6E) formed on each side thereof and positioned distally adjacent toa cut-out (only one cut-out 502 c is shown in FIG. 6A, as will bediscussed in more detail below). Each cam 512 d, 514 d will act againstthe abutment 503 a formed on the inner tube 502 to push the inner tube502 distally relative to the outer tube 504. As a result, a bone anchorcan be engaged between the distal ends 502 d, 504 d of the inner andouter tubes 502, 504. In order to release the bone anchor, the arms 512,514 can be moved back to the transverse position, in which the arms 512,514 extend away from and at an angle relative to a longitudinal axis ofthe outer tube 504. The cams 512 d, 514 d will thus return to theiroriginal position, allowing the inner tube 502 to move in a proximaldirection relative to the outer tube 504.

FIG. 6A illustrate an exemplary boss 514 b formed on arm 514. As shown,the boss 514 b is in the form of a generally circular protrusion or apin formed on an outer-facing surface of the distal end 514 d of arm514. The boss 514 b is configured to extend into a circular orsemi-circular cut-out 504 c ₁ formed in the outer tube 504. As shown inFIG. 6A, the cut-out 504 c ₁ is located a distance distally apart fromthe proximal end 504 p of the outer tube 504. As shown in FIGS. 6B, 6D,and 6E, a second boss 512 b is formed on an outer surface of arm 512,and a second cut-out 504 c ₂ is formed in an opposed side of the outertube 504 for rotatably seating the second boss 512 b.

FIG. 6A also illustrates an exemplary protrusion 512 c formed on aninner-facing surface of the distal end 512 d of arm 512. The shape ofthe protrusion 512 c can vary depending on the configuration of thecorresponding cut-out formed in the inner tube 502. In an exemplaryembodiment, the protrusion 512 c is configured to alter a size of thecorresponding cut-out formed in the inner tube 502 as the arms 512, 514are moved between the locked and unlocked positions. This willfacilitate movement of the inner tube 50 proximally to the originalunlocked position, thus allowing detachment of a bone anchor fromengagement between the distal ends 502 d, 504 d of the inner and outertubes 502, 504. The protrusion 512 c can also act as a mechanical stopto limit rotation of the arms 512, 514 between the unlocked and lockedpositions. In the embodiment shown in FIG. 6A, the protrusion 512 c hasa circular portion and a flattened portion formed around a perimeterthereof. FIG. 6A also illustrates a corresponding cut-out 502 c aimed inthe inner tube 502. As shown, the cut-out 502 c extends radially arounda portion of the proximal end 502 p of the inner tube 502 to form aspring arm 506 a on the proximal-most end of the inner tube 502. Whilenot shown, a complementary cut-out is formed in an opposed side of theproximal end 502 p of the inner tube 502 to form a second spring arm.The spring arm 506 a is configured to flex to allow a size of thecut-out 502 c to be altered when the protrusion 512 c is rotatedtherein. In particular, the cut-out 502 c includes a circular portionthat seats the circular portion of the protrusion 512 c. When the aims512, 514 are positioned to extend transversely outward from the outertube 504, i.e., when the arms 512, 514 are positioned at an anglerelative to a longitudinal axis of the outer tube 504 as shown in FIG.6D, the protrusion 512 c will be in the first unlocked position. In thisposition, the circular portion of the protrusion 512 c will rest withinthe circular portion of the cut-out 502 c. The flattened portion of theprotrusion 512 c will not be in contact with any portion of thecorresponding cut-out 502 c. When the arms 512, 514 are pivoted towardthe outer tube 504 to longitudinally align the arms 512, 514 with theouter tube 504, as shown in FIG. 6E, the protrusion 512 c will rotatewithin the cut-out 502 c. The flattened portion of the protrusion 512 cwill abut against a perimeter of the cut-out 502 c, forcing the springarm 506 a proximally away from the remainder of the inner tube 504. Theprotrusion 512 c will thus increase a length of the cut-out 502 c, asmeasured in a proximal-distal direction. This will cause the distal end502 d of the inner tube 502 to move distally toward the distal end 504 dof the outer tube 504, further facilitating engagement of a bone anchorbetween the distal ends 502 d, 504 d of the inner and outer tubes 502,504. When the arms 512, 514 are moved back to the transverse position,in which the arms 512, 514 extend away from and at an angle relative toa longitudinal axis of the outer tube 504, the protrusion 512 c willreturn to its original position allowing the spring arm 506 a to recoil.The recoil will help pull the inner tube 502 proximally to allowdetachment of a bone anchor engaged between the distal ends 502 d, 504 dof the inner and outer tubes 502, 504. While not shown, a person skilledin the art will appreciate that the distal end 514 d of arm 514 caninclude a protrusion formed on an inner surface thereof, and the innertube 502 can include a second cut-out formed on an opposed side of theinner tube 502 and defining a second spring arm.

The locking mechanism 510 can also include a feature that is effectiveto maintain the locking mechanism 510 in the locked position. Whilevarious techniques can be used, in one exemplary embodiment a proximalportion of one or both arms 512, 514 can include one or more teethformed thereon and configured to engage corresponding teeth formed onthe proximal end 504 p of the outer tube 504. For example, an innersurface of one of the arms 512, 514 can include teeth (not shown) formedadjacent to but distal of the proximal end 512 p, 514 p thereof. Theouter tube 504 can include corresponding teeth 504 t formed thereon, asshown in FIG. 6A, for mating with the teeth on the arm(s) 512, 514 whenthe arm(s) 512, 514 is in the locked position. One or both arms 512, 514can also include a handle 512 h, 514 h formed on a proximal-most endthereof to facilitate grasping of the arms 512, 514, and to release theaims 512, 514 from the locked position. When the arms 512, 514 are inthe locked position, the handles 512 h, 514 h will be positionedproximal to the proximal end 504 p of the outer tube 504, as shown inFIG. 6C. In order to release the arms 512, 514 from engagement with theouter tube 504, the handles 512 h, 514 h can be squeezed together topush the teeth on the arm(s) 512, 514 away from the teeth 504 t on theouter tube 504. As a result, the arms 512, 514 can be pivoted away fromthe outer tube 504 to the unlocked position, shown in FIG. 6B. A personskilled in the art will appreciate that a variety of other techniquescan be used to releasably maintain the locking mechanism 510 in a lockedposition, and that the locking mechanism 510 can have a variety of otherconfigurations.

FIGS. 7A and 7B illustrate another exemplary bone anchor 600 that ismatable to a distal end of the bone anchor extensions of FIGS. 5A-6E. Byway of non-limiting example, the bone anchor 600 is shown coupled to thebone anchor extension 500 of FIGS. 6A-6E, however the bone anchorextensions disclosed herein are not limited to use with the illustratedbone anchor 600 but instead may be configured for use with any type ofbone anchor, e.g., bone screw or hook; mono-axial or polyaxial. The boneanchor 600 is similar to the bone anchor 250 previously described withrespect to FIG. 3B, and generally includes a bone engaging portion,e.g., a threaded shank 604, and a receiving member or head 602 locatedon a proximal end of the shank 604. The head 602 includes a groove 603a, 603 b formed on an outer surface of each arm 602 a, 602 b thereof forreceiving a corresponding lip formed on an inner surface of a distal endof the outer tube 504. The lips on the outer tube 504 can be positionedwithin the grooves 603 a, 603 b on the head 602, as shown in FIG. 7A, bypositioning the opposed arms 505 a, 505 b of the outer tube 504 off-setfrom the arms 602 a, 602 b of the head 602 and rotating the bone anchorextension 500 to slide the lips into the grooves 603 a 603 b. Oncemated, the locking mechanism 510 (not shown) can be actuated to move theinner tube 502 to the distal locked position such that the distal end502 d of the inner tube 502 abuts against a proximal-facing surface ofeach arm 505 a, 505 b of the head 502. The head 502 will thus becaptured between the distal ends 502 d, 504 d of the inner and outertubes 502, 504, thereby preventing separation of the bone anchorextension 500 and bone anchor 600 until desired.

In use, the various bone anchor extensions disclosed herein can providea percutaneous pathway between a skin incision and a bone anchor tofacilitate delivery of instruments, spinal fixation elements, and/orcomponents of the bone anchor, such as a closure mechanism, to the boneanchor. In particular, a bone anchor extension can be mated to a boneanchor by actuating the locking mechanism to move it to the lockedposition, thereby capturing the bone anchor at the distal end of thedevice. The device, with the bone anchor attached thereto, can be passedthrough a skin incision to position the bone anchor adjacent to bone.The lumen extending through the bone anchor extension will provide apathway to the receiving member of the bone anchor. The pathway canallow a driver or other tools to be inserted therethrough for drivingthe bone anchor into bone, and it can also facilitate delivery of afastening mechanism, such as a threaded cap or set screw, to the boneanchor. The bone anchor extension can include various features tofacilitate delivery of a driver, fastening mechanism, or otherinstrument or device. For example, the inner lumen of the bone anchorextension can include threads formed therein for mating withcorresponding threads formed on a driver mechanism or other instrumentor device. The opposed longitudinal slots formed in the bone anchorextension can also be aligned with opposed recesses provided in thereceiving member. Alignment of the slots with the recesses canfacilitate delivery of a spinal fixation element, such as a spinal rod,to the bone anchor prior to delivering of a fastening mechanism. Methodsand devices for spinal fixation element placement are disclosed incommonly owned co-pending U.S. patent application Ser. No. 10/737,537,filed on Dec. 16, 2003, entitled Method and Devices for Spinal FixationElement Placement (Attorney Docket No. 101896-210) and commonly ownedco-pending U.S. patent application Ser. No. 10/738,130, filed on Dec.16, 2003, entitled Method and Devices for Minimally Invasive SpinalFixation Element Placement (Attorney Docket No. 101896-209), both ofwhich are incorporated herein in by reference in their entireties. Oncethe bone anchor is implanted, and the procedure is complete, i.e., othercomponents are mated to the bone anchor as may be necessary, the lockingmechanism can be returned to the unlocked position, thereby allowing thebone anchor extension to be disengaged from the bone anchor and to beremoved from the patient's body.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1-20. (canceled)
 21. A bone anchor extension, comprising: an outer tubehaving proximal and distal ends with a lumen extending therebetween; aninner tube at least partially disposed within the lumen in the outertube, the inner tube having proximal and distal ends with a lumenextending therebetween; and a locking mechanism pivotally coupled to theouter tube at a first pivot point and pivotally coupled to the innertube at a second pivot point, the second pivot point being distal of thefirst pivot point, and the locking mechanism being configured to advancethe inner tube distally relative to the outer tube to engage a boneanchor between the distal ends of the outer and inner tubes.
 22. Thebone anchor extension of claim 21, wherein the first pivot point isproximal to the proximal end of the inner tube.
 23. The bone anchorextension of claim 21, wherein the first pivot point is approximatelycentrally disposed along a centerline of the outer tube.
 24. The boneanchor extension of claim 21, wherein a proximal end of the lockingmechanism is positioned on one side of the outer tube and a distal endof the locking mechanism is positioned on an opposite side of the outertube when the locking mechanism is in a locked position.
 25. The boneanchor extension of claim 21, wherein the locking mechanism comprises:an arm having a proximal end, a distal end, and a central portion; alinkage having a proximal end and a distal end; wherein the centralportion of the arm is pivotally coupled to the outer tube at the firstpivot point, the distal end of the linkage is pivotally coupled to theinner tube at the second pivot point, and a distal end of the arm ispivotally coupled to a proximal end of the linkage at a third pivotpoint.
 26. The bone anchor extension of claim 21, wherein the inner tubefurther comprises a relief slit formed thereon and configured to providerelief to the stress applied to the locking mechanism when the lockingmechanism is in a locked position.
 27. The bone anchor extension ofclaim 26, wherein the relief slit is a spiral cut slit extendingradially around the proximal end of the inner tube.
 28. The bone anchorextension of claim 21, wherein the distal end of the outer tube isconfigured to rotate relative to a bone anchor to engage a bone anchor.29. The bone anchor extension of claim 21, wherein the distal end of theouter tube is configured to flex apart in a radial direction to engage abone anchor.
 30. The bone anchor extension of claim 21, wherein thedistal end of the inner tube comprises a contact surface configured toengage a generally arcuate contact surface of a bone anchor.
 31. Thebone anchor extension of claim 21, wherein at least one of the innertube and the outer tube includes an anti-rotation mechanism configuredto inhibit rotation of a bone anchor relative to the inner and outertubes.
 32. The bone anchor extension of claim 21, wherein the outer tubeis sized to span from at least a skin incision in a patient to apredetermined site proximate a spine of the patient.
 33. A bone anchorextension, comprising: an outer tube having proximal and distal endswith a lumen extending therebetween; an inner tube at least partiallydisposed within the lumen in the outer tube, the inner tube havingproximal and distal ends with a lumen extending therebetween; and alocking mechanism pivotally coupled to each of the outer tube and theinner tube, the locking mechanism having a proximal portion and a distalportion, wherein the locking mechanism is movable between a firstposition, in which the locking mechanism extends longitudinally relativeto a longitudinal axis of the outer tube and the proximal portion ispositioned on one side of the outer tube and the distal portion ispositioned on an opposite side of the outer tube, and a second positionin which the locking mechanism extends transversely outward relative toa longitudinal axis of the outer tube.
 34. The bone anchor extension ofclaim 33, wherein the locking mechanism comprises: an arm having aproximal end, a distal end, and a central portion; a linkage having aproximal end and a distal end; wherein the central portion of the arm ispivotally coupled to the outer tube, the distal end of the linkage ispivotally coupled to the inner tube, and a distal end of the arm ispivotally coupled to a proximal end of the linkage.
 35. The bone anchorextension of claim 33, wherein the proximal portion of the lockingmechanism is pivotally coupled to the outer tube and the distal portionof the locking mechanism is pivotally coupled to the inner tube suchthat pivotal movement of the locking mechanism advances the inner tubedistally relative to the outer tube to engage a bone anchor between thedistal ends of the outer and inner tubes.
 36. The bone anchor extensionof claim 33, wherein a location where the proximal portion of thelocking mechanism is pivotally coupled to the outer tube is proximal tothe proximal end of the inner tube.
 37. The bone anchor extension ofclaim 33, wherein a location where the proximal portion of the lockingmechanism is pivotally coupled to the outer tube is approximatelycentrally disposed along a centerline of the outer tube.
 38. The boneanchor extension of claim 33, wherein the inner tube further comprises arelief slit formed thereon and configured to provide relief to thestress applied to the locking mechanism when the locking mechanism is ina locked position.
 39. The bone anchor extension of claim 38, whereinthe relief slit is a spiral cut slit extending radially around theproximal end of the inner tube.
 40. The bone anchor extension of claim33, wherein the outer tube is sized to span from at least a skinincision in a patient to a predetermined site proximate a spine of thepatient.